The present invention relates to fetal monitoring; more particularly, the present invention relates to improvements in fetal electrode applicators.
U.S. Reissue Pat. No. 28,990 discloses an electrode structure used in particular for detecting fetal ECG and which has found wide acceptance for direct fetal heartbeat monitoring. The electrode structure per se includes a coil electrode mounted on the distal face of a cylindrical, insulating electrode holder. A spade shaped reference electrode is mounted on the opposite, proximal face of the cyclindrical electrode holder. The electrode is disposed in the distal end of a guide tube adapted to be inserted through the vagina and cervix of a woman in labor. A drive tube is disposed within the guide tube and has a distal end provided with a notch to receive the reference electrode of the electrode structure. The drive tube extends through the guide tube to a proximal end which extends outwardly of the proximal end of the guide tube so that it may be grasped by a physician. Once the physician has introduced the distal end of the guide tube through the vagina and cervix to the fetal scalp, the physician rotates the drive tube to impart a rotational motion to the electrode structure thus to cause the coil electrode to affix to the fetal scalp.
With this prior art arrangement, the physician is enabled easily to sense the point at which the coil electrode has become fully embedded in the fetal scalp. This is important in that excessive rotation of the electrode holder may cause a laceration of the fetal scalp, while insufficient rotation of the coil electrode may result in its coming loose from the fetal scalp resulting in a loss of the hearbeat signal and possible injury to maternal tissues.
In order to render such a device easier to use, it is desirable to eliminate the need for the drive tube to be rotated manually. In U.S. patent application Ser. No. 21,550 filed Mar. 20, 1979 in the name of Edward D. Hon, a plunger is mounted within the guide tube and, when moved toward the distal end of the guide tube by a force applied thereto by the physician, causes a helical thread-type means to rotate the holder and the spiral retaining coil into the fetal epidermis. However, the use of this arrangement tends to reduce the physician's ability to sense when the coil electrode has been fully embedded in the fetal scalp, or whether it has penetrated the scalp at all.